Conventional bicycle frames are designed to be as light and as rigid as possible. They rely on this rigidity to efficiently transfer the rider's pedaling efforts to the rear tire. Good frame rigidity is also the foundation for a good handling bicycle. However, rigid frames have one major negative side effect, rider discomfort. Any bump encountered by the rear tire sends a shock force through the frame directly to the seat where it is felt by the rider.
There are two possible solutions to the problem of rider discomfort. The first solution involves the addition of a motorcycle-style suspension system to the bicycle frame. A second solution relies on the addition of a shock absorption device to the bicycle seatpost.
Motorcycle-style suspension systems have several problems. First, these systems are very heavy and thus require the rider to expend more energy to propel the bicycle. In addition, they reduce the frame's rigidity and thus its ability to efficiently transfer the rider's pedaling efforts to the rear fire. The added weight and loss of rigidity also reduce the bicycle's handling quality. Finally, custom-made suspension-frame bicycles are among the most expensive bicycles on the market. Considering these inherent problems, frames with motorcycle-style suspension systems are not a viable solution to the problem of rider discomfort.
A shock absorption device integrated into the seatpost of a bicycle offers increased rider comfort without the negative side effects of a motorcycle-style suspension system. Suspension seatposts are lightweight, inexpensive, and adaptable to nearly any existing bicycle. They advantageously allow use of conventional bicycles with lightweight, rigid, and efficient frames. And, when designed properly, they absorb bump forces transmitted from the rear tire, thus increasing rider comfort.
A search of prior art revealed two U.S. Patents relating to suspension seatposts for bicycles. The first seatpost, U.S. Pat. No. 4,456,295 to Nicholas Francu, shows a seat, suspended by numerous springs, that travels along a vertical path. The second seatpost, U.S. Pat. No. 4,736,983 to Raymond Furbee, shows a seat, suspended by a single spring, that travels along a downward, forward path determined by the angle of the bicycle frame's seat tube. Both of these seatposts are inherently flawed. Neither design situates the shock absorption device in line with the bump forces. As the rear tire of a bicycle encounters obstacles, it causes the bicycle frame to pivot around the axle of the front wheel. This pivoting action creates an upward,forward-moving bump force at the bicycle seat. Therefore, to avoid binding, a suspension seatpost must be designed with a shock absorption device that allows the seat to travel along a downward, rearward path.